According to the related art, a working tool of a construction machine is designed to be driven by a mechanical hydraulic system. Such a mechanical hydraulic system has a structure in which a main hydraulic pressure supplied to a hydraulic cylinder connected to a working tool of a construction machine is controlled by opening or closing a spool of a mechanical main control valve (MCV) with a pilot hydraulic pressure from a valve located at a joystick lever for controlling a pilot hydraulic pressure.
FIG. 1 is a diagram of a mechanical hydraulic system according to the related art.
As illustrated in FIG. 1, the mechanical hydraulic system according to the related art includes an engine 110, a pump 120, a hydraulic pressure valve 130 connected to a hydraulic joystick lever 131, a hydraulic main control valve 140 and a hydraulic cylinder 150. Here, the hydraulic main control valve 140 includes a spool 141 and is connected to the hydraulic cylinder 150 through an orifice 142.
The pump 120 operated by the engine 110 supplies a working fluid 121, that is, a hydraulic pressure to the hydraulic pressure valve 130 and the hydraulic main control valve (MCV) 140. The mechanical hydraulic system according to the related art is designed such that a working tool of a construction machine is driven by mechanically adjusting a hydraulic pressure.
A user manipulates the hydraulic joystick lever 131 to control the hydraulic cylinder 150. To this end, the hydraulic pressure valve 130 supplies a pilot hydraulic pressure supplied from the pump 120 to the hydraulic MCV 140 according to the manipulation of the hydraulic joystick lever 131 by the user. Then, the hydraulic pressure from the hydraulic pressure valve 130 is used to open or close the spool 141 of the mechanical MCV 140 and thus change a main hydraulic pressure supplied to the hydraulic cylinder 150 connected to the working tool.
Meanwhile, an operational behavior of the working tool against the hydraulic joystick lever 131 is determined according to characteristics of mechanical elements connected to the mechanical hydraulic system. For example, the behavior is determined according to a notch shape of the spool 141 in the hydraulic MCV 140 or characteristics of parts including an orifice 142 installed in a hydraulic pressure passage and the like. Such a part is a mechanical element and has fixed characteristics, and thus cannot have a variable structure to correspond to various behaviors during an operation thereof.
Thus, in the construction machine including such a mechanical hydraulic system according to the related art, a behavior of the hydraulic joystick lever 131 and the behavior of a working tool need to be determined by compromising a comfortableness of an operator and an abrupt operation (for example, a beating operation of a bucket) efficiency which are incompatible at a proper point. If the behavior is set too softly, considering a comfortableness of an operator, a beating operation may be problematic. The construction machine according to the related art employs a structure where a comfortableness of an operator is lowered to some degree and instead, a response of the hydraulic joystick lever 131 is increased to a proper point high enough not to cause a problem to an operation.
In particular, in a beating operation, a construction machine (for example, a wheel loader and an excavator) excavates an object having a certain degree of viscosity. For example, the viscous object to be excavated may include mud, livestock night soils, and concrete. In this case, an operation method for a construction machine for dropping residue stuck to a bucket due to viscosity by shaking the bucket upward and downward at a dumping place after an operator loads an object to be excavated in a bucket is necessary.
Here, the part shaking the bucket in the beating operation needs to be set to have a maximum value for changing a hydraulic pressure in order to show a maximum effect. That is, a structure for maximally increasing a response of the hydraulic joystick lever 131 may have an optimum operation efficiency in a beating operation. Meanwhile, if a response of the working tool is set only for a beating operation, vibrations are caused in the vehicle even in an operation other than the beating operation, hampering a comfortableness of the operator.
As described above, if a comfortableness of an operator is enhanced by making a behavior of a construction machine soft in the mechanical hydraulic system according to the related art, an efficiency of a specific operation, such as a load beating operation, which shows an abrupt response is lowered in response.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.